KW Micro Power designs and manufactures high power density Auxiliary Power Units (APUs) for commercial aviation and military applications. They are a small Florida-based manufacturer looking for new, cutting-edge solutions. Over the past five years, Enrique Enriquez, the president of KW Micro Power, has worked tirelessly to create a microturbine generator roughly the size of a microwave oven that can crank out more power than systems ten times as large.
Enriquez is no stranger to aerospace design and manufacturing. Over his long and successful career, he has led engineering teams in Rolls-Royce, worked with DARPA on the first drone propulsion systems, and bought the second 3D printing system ever manufactured by Stratasys. But he is totally astonished by the capabilities of contemporary design software and additive manufacturing systems. “I think this is like the renaissance of engineering,” he mentions. Additive manufacturing became an important tool in the development of the microturbine generator.
A key component of KW Micro Power’s airborne microturbine is the generator housing. The engineers of KW Micro Power, nTopology, and VELO3D created a housing that is not only much lighter than the original design and manufacturable as one piece with minimal support structures but also features internal conformal channels for cooling the engine and preheating the fuel.
Lightweighting APUs for aerospace
For landbound applications, weight is not a big concern. Yet, for APUs on board an aircraft or drone, lightweighting is a number one priority — and every pound counts. The engineering team managed to reduce the weight of the generator’s housing by 44% — from approximately 10.4 kg down to 5.9 kg. This result surpassed the expectations of the KW Micro Power team. “I would be more than happy with just 20-25% weight reduction!” Enriquez mentioned.
An added bonus: the housing, which was originally CNC machined, can be manufactured in a single piece with metal Additive Manufacturing. The part consolidation available through additive manufacturing improves machine reliability. For example, when an engine spins at 90,000 rpm, everything needs to be precisely aligned. A single piece eliminates any alignment concerns.
Redesigning the part for additive manufacturing was a straightforward process. To achieve these results, Enriquez’s team followed a Field-Driven Design approach:
–They first confirmed that the loads on the housing were relatively small using nTop Platform’s integrated static and modal analysis simulation tools.
–Then they removed unnecessary material to create a hollow shell with a variable wall thickness.
–Finally, they smoothed the internal geometry to ensure that it required no support structures during manufacturing with VELO3D’s metal AM process.
The whole process required only a few simple design blocks in nTop Platform and took less than one day’s work before the part was ready to manufacture. It also opened up opportunities to add additional functionality, such as conformal cooling channels for heat management.
Cooling electric machines using conformal channels
Thermal management is one of the main size constraints of electric machines. Simply put, better cooling means more power.
Efficient cooling minimizes generator hot spots, enables higher current densities, reduces ohmic losses, and lessens heat stress on machine components — especially the windings and the magnets. In power generation systems, cooling increases efficiency and torque, reduces weight, extends machine life, and lowers maintenance costs.
In this project, the hollow structure that was initially conceived to reduce the weight of the motor casing could also function as a cooling channel.
Enriquez’s team has experimented in the past on test parts with internal spirals with great success. This was, however, the first time they applied the concept to a component of their microturbine.
The team experimented with different cooling mediums. One appealing option was engine fuel. Using fuel not only cools the engine with a liquid that is already onboard the aircraft, but also preheats the fuel, increasing the efficiency of the combustion process.
From design to manufacturing
The new design of the generator housing was manufactured by VELO3D on the company’s Sapphire metal 3D printing system in Aluminum F357 — a foundry-grade aluminum alloy that can be anodized and is certified for mission-critical applications.
The capabilities of VELO3D’s LPBF additive manufacturing system were taken into consideration during the design phase to create a part that is manufacturable and with minimal support structures and post-processing requirements.
VELO3D’s SupportFree technology and tight control of processing parameters was a good match for the level of control offered by the nTop Platform.
The next steps
KW Micro Power is planning to launch its lightweight aerospace-grade microturbine in 2021. However, new ideas to increase the functionality of each component of the power generation system keep coming. For example, the design team is now examining how to use lattice structures to further reduce the weight of the airborne model or how to embed electronic sensors and filters to monitor the performance of the generator in real-time.
Velo3D
www.velo3d.com
nTopology
ntopology.com
Filed Under: Make Parts Fast